AR-15 Noob in need of advice: Bushmaster 16" HBAR M4 Dissipator

[Jordan85]

I am looking to trade into my first AR and I received an offer involving this gun. Can somebody tell me a little bit about this gun? http://www.bushmaster.com/catalog_xm15_BCWA3S16D.asp

What are the advantages/disadvantages of this "dissipator" set-up vs. a "mid-length" or "carbine" M4 set-up?

From what I have researched, the two main differences are the longer sight radius on the Dissipator, and the "Dissipator’s Gas Block is located behind the front sight base, and under the full length handguards. This configuration offers improved heat dissipation, and therefore the model’s name"

Ok, I understand dissipating heat is a good thing for numerous reasons. But, are there any disadvantages to this set-up? Does it mess up the balance of the gun? Does this mean this model is required to have full length handguards?

Also, the seller mentioned the barrel is "target crowned no flash." I'm assuming this means the barrel isn't threaded and does not have the option to add a flash suppressor to it.... Am I correct in this understanding?

Anything else I should know about this model going into this deal? My knowledge of ARs is admittedly small, but I am basically wondering if there are any limitations imposed by going w/ this set-up. At this point, I don't know enough about the AR to have a strong criteria list, but I would prefer not to get into one of those "if I had known then what I know now" situations where I am stuck w/ a niche rifle; I would like to go with a set-up that will allow me to grow with it as I begin to gain an understanding and criterion of what I want/need in my AR.

Also, some suggestions on what a trade like this may be worth in value?

Thanks for the help in advance. Everyone is always very helpful at THR, and I have no doubt that this post will receive the same attention. There are some very informative and helpful people here at THR, and I always appreciate the knowledge I gain from others browsing this forum

 

[highorder]

The dissapator is of little value (to me) in the age of the Mid-length gas system.

With the Mid length, you get a longer sight radius than a carbine(doesn't everyone have an Aimpoint or EOtech anyway?) and a smoother action, with less bolt abuse and fouling.

Does this mean this model is required to have full length handguards?

in short, no. you can use carbine, midlength, or rifle length free float tubes as well as full length handguards (picatinny or standard)

 

[Jordan85]

(doesn't everyone have an Aimpoint or EOtech anyway?)

Not if you are buying your first AR and are me.... So in reality I prob will end up using iron sites for at lease a few months.

 

[highorder]

In those few months, you will have to deal with the minute, theoretical difference in sight radii.

I still don't see any point in a dissapator unless you plan to cut, crown, and SBR it later...

By this I mean that I am very happy with my Mid Length from Del-ton.

 

[Taurus 617 CCW]

I would suggest taking a serious look at our rifles. Here is a short specs comparison over the Bushmaster you are considering.

Our rifles have a ceramic coating on the inside and outside of the gun which allows it to dissipate heat 40% faster than an uncoated gun. The inside ceramic coating acts increases abrasion resistance and allows the rifle to operate without the use of any lubrication (that's right, I said oil free). A combination of components that we chose including our flash suppressing/recoil dampering muzzle break, we have eliminated 60% of motion in the gun. That means there is virtually no muzzle rise. We also have very nice triggers installed by our master pistolsmith which are much improved over the mil-spec triggers.

Our guns come these standard accessories: Spectre Gear M.O.U.N.T. Sling, OTIS Tactical Cleaning Kit, (2) Cammenga Easy Mags, Operators Manual, Padlock, Locking Hard Case, and our unconditional lifetime guarantee. If you were to add up the additional components and gunsmithing we do on our guns it would cost an extra $800-1000 though the custom shop of your choice. Check out our rifles at www.nextgenerationarms.com or PM me if you have further questions.

 

[Jordan85]

Can somebody explain how the dissipator is different from mid-length etc. set-up?

 

[highorder]

This will save a good deal of time for you. Enjoy!

http://thehighroad.org/showthread.php?t=199626

 

[Jordan85]

Thanks for the offer Taurus, but I think your guys' work is a little beyond my means at this point. I am trying to stay in the $700-$800 range, or if possible, trade into one

 

[H2O MAN]

There is nothing wrong with a BM Dissi, I've owned two and liked them.

I suggest that you shop around for a slightly used one on the cheap though...

 

[twofourthree73]

I'd avoid that rifle just for the fact that it's an HBAR and will be very front heavy, that and the non-threaded muzzle will limit your options. You can put any length free float hand guards on it, but a carbine length will leave the gas block exposed.

I got my CMMG Mid lengh carbine for $850 new after shipping and transfer fees. Bought the lower first and then ordered the upper.

You aren't going to have a significant advantage with rifle length sight radius over a mid length with open sights for any shooting under 200 yards. You be come the most important piece of the puzzle at that range, not your sight radius.

 

[Jordan85]

after doing a little research, I am beginning to understand the differences. Correct me if I am wrong: it appears that the dissipator uses the carbine gas system, which is shorter has somewhat more violent recoil than the mid-length or rifle gas system. I think I am wrong, but wouldn't that just make the dissipator an M4 carbine w/ the FSB pushed out to the end of the barrel?? I'm confused

 

[Milky]

Yes and you also get rifle length handguards.

Some manufacturers let you choose mid-length, carbine, or rifle length gas system on the dissipator setup with the longer sight radius and full length handguards.

 

[H2O MAN]

I have read on some of the forums that are more dedicated to AR type rifles that the
best all-around, general purpose upper is a 16.0" barrel with a mid-length gas system.
A standard profile barrel is also recommended because it's lighter.

If you can find one in your price range, that may be your best option.

 

[highorder]

The dissapator has a gas block under the handguards, and a dummy FSB (w/o gas) at the end of the handguards.

Correct me if I am wrong: it appears that the dissipator uses the carbine gas system, which is shorter has somewhat more violent recoil than the mid-length or rifle gas system.

correct.

 

[Jordan85]

So, hypothetically, if you got added carbine length handguards and pushed the FSB back some it would now be a plain-ol' M4 Carbine?

 

[highorder]

So, hypothetically, if you got added carbine length handguards and pushed the FSB back some it would now be a plain-ol' M4 Carbine?

Basically, yes. you would need to remove the carbine gas block and install a handguard retainer; then reinstall the gas block.

Or, simply use a free float tube; whatever length you like. My thought is this: if you are going to use a FF tube on a 16" bbl rifle, the mid length gas system is better in every way.

 

[Jordan85]

if you are going to use a FF tube on a 16" bbl rifle, the mid length gas system is better in every way.

So where does the dissipator shine then? What is the advantage the dissipator has over a standard M4 carbine / mid-length. Since these guns could always push the FSB forward and now have the advantageous longer sight radius, there has to be other advantages the dissipator offers, right?

 

[highorder]

So where does the dissipator shine then?

Easy, they don't.

The Dissapator was invented before the mid length was introduced. I never saw an advantage to the dissapator; it looks like a configuration without a purpose. FWIW, the carbine gas system was invented for 11" bbls, not the 16" carbine.

I don't know what else there is to say. If you like to look of the dissy, go ahead.

 

[Jordan85]

I never saw an advantage to the dissapator; it looked like a configuration without a purpose.

Thoughts anyone???

Sometimes I just like to play the role of intermediary and let the more knowledgeable folks slug it out while I sit back and take notes

 

[highorder]

Sometimes I just like to play the role of intermediary and let the more knowledgeable folks slug it out while I sit back and take notes

Great, now I get to square off against whatever gold gloves SOCOM guy that happens by...

 

[Jordan85]

lol, but these small 'conflicts' are where some of the best knowledge comes from (assuming they keep it civil)

 

[Timradcliffe345]

The dissipator does indeed serve a purpose: It offers a longer sight radius.

If you want the best of both worlds, get a 16" AR w/midlength gas system and rifle length handguards.

Just like this:

http://cmmginc.secure-mall.com/shop/images/667.jpg

It's a nice setup, especially if you are planning on using the irons.
I would also recommend buying the upper and lower separately.

Don't forget to purchase a high quality BCG such as LMT or BCM. Then you should be good to go. Good luck.

 

[Jordan85]

The dissipator does indeed serve a purpose: It offers a longer sight radius.

But I don't understand why any other 16" AR w/ midlength gas system could not achieve this same sight radius by merely pushing the front iron forward to the end of the barrel. Is there a reason why the front sight couldn't just be moved forward and viola we have longer sight radius.

That is why I was wondering if there was another advantage this system offers...

 

[Matt-man]

This is what a Dissipator looks like under the handguards:


There are two gas blocks on a rifle like this. The one to the rear is the real gas block, which has the gas port underneath it. The front one exists solely to support the front sight. In this case the rear gas block is in the normal position for a carbine-length gas system. The front one is in the normal position for a rifle-length gas system. Mid-length gas systems have the gas block in the middle.

You can't just push the front sight out to the end of a 16" barrel because it's usually attached to the gas block, and putting the gas block out there screws up the timing of the gas operation. The gun won't run right if you do that.

 

[C-grunt]

If youre going to have the full length handguards, whats the advantage of a mid lenght gas system over the full rifle length??

Just curious, not trying to thread jack.